Animating a bone to turn 360° doesn't rotate correctly
I guess if you keyframe it in the 3D view it won't interpolate correctly because either it doesn't know in what direction it is supposed to go or Quaternion interpolation is messy, don't ask me why.
The easiest way to do it is to use the N &gt; Item &gt; Transform panel, switch Quaternion to XYZ Euler, and keyframe a rotation of 0/0/0° at frame 0, and 0/360/0° at frame X (I keyframed the bone in Pose mode, if you want to keyframe the armature in Object mode it will be 0/0/360°):